Array.prototype[Symbol.iterator]()

¥Syntax

array[Symbol.iterator]()

¥Parameters

没有任何。

¥None.

¥Return value

与 Array.prototype.values() 返回值相同：一个新的 可迭代的迭代器对象，它生成数组中每个索引的值。

¥The same return value as Array.prototype.values(): a new iterable iterator object that yields the value of each index in the array.

¥Examples

¥Iteration using for...of loop

请注意，你很少需要直接调用此方法。[Symbol.iterator]() 方法的存在使得数组 iterable，像 for...of 循环这样的迭代语法会自动调用该方法来获取要循环的迭代器。

¥Note that you seldom need to call this method directly. The existence of the [Symbol.iterator]() method makes arrays iterable, and iterating syntaxes like the for...of loop automatically call this method to obtain the iterator to loop over.

HTML

<ul id="letterResult"></ul>

JavaScript

const arr = ["a", "b", "c"];
const letterResult = document.getElementById("letterResult");
for (const letter of arr) {
  const li = document.createElement("li");
  li.textContent = letter;
  letterResult.appendChild(li);
}

结果

¥Result

¥Manually hand-rolling the iterator

你仍然可以手动调用返回的迭代器对象的 next() 方法，以实现对迭代过程的最大控制。

¥You may still manually call the next() method of the returned iterator object to achieve maximum control over the iteration process.

const arr = ["a", "b", "c", "d", "e"];
const arrIter = arr[Symbol.iterator]();
console.log(arrIter.next().value); // a
console.log(arrIter.next().value); // b
console.log(arrIter.next().value); // c
console.log(arrIter.next().value); // d
console.log(arrIter.next().value); // e

¥Handling strings and string arrays with the same function

因为 strings 和数组都实现了可迭代协议，所以可以设计一个通用函数来以相同的方式处理两个输入。这比直接调用 Array.prototype.values() 要好，后者要求输入是一个数组，或者至少是一个具有这种方法的对象。

¥Because both strings and arrays implement the iterable protocol, a generic function can be designed to handle both inputs in the same fashion. This is better than calling Array.prototype.values() directly, which requires the input to be an array, or at least an object with such a method.

function logIterable(it) {
  if (typeof it[Symbol.iterator] !== "function") {
    console.log(it, "is not iterable.");
    return;
  }
  for (const letter of it) {
    console.log(letter);
  }
}

// Array
logIterable(["a", "b", "c"]);
// a
// b
// c

// String
logIterable("abc");
// a
// b
// c

// Number
logIterable(123);
// 123 is not iterable.

¥See also

• core-js 中 Array.prototype[Symbol.iterator] 的 Polyfill
• 索引集合 指南
• Array
• Array.prototype.keys()
• Array.prototype.entries()
• Array.prototype.values()
• TypedArray.prototype[Symbol.iterator]()
• String.prototype[Symbol.iterator]()
• Symbol.iterator
• 迭代协议